


Natural (It's all in the chemistry)

by Trojie



Series: Fics for SPNVerse Challenges [6]
Category: Supernatural
Genre: Alpha/Beta/Omega Dynamics, Bunker Fic, Dirty Talk, First Time, Human Castiel, Implied Mpreg, Knotting, Loss of Virginity, M/M, Mating Cycles/In Heat, Threesome - M/M/M
Language: English
Status: Completed
Published: 2013-09-15
Updated: 2013-09-15
Packaged: 2017-12-26 17:06:47
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 6,392
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/968406
Author URL: https://archiveofourown.org/users/Trojie/pseuds/Trojie
Summary: <blockquote class="userstuff">
              <p>Why did they not give him this talk when he turned human, when it could have just been another orientation lecture and not the most loaded of all loaded questions, with Cas in heat and Dean and Sam getting closer and closer to full-blown rut the longer they spend around him?</p>
            </blockquote>





	Natural (It's all in the chemistry)

**Author's Note:**

> Post S8 Wincestiel with newly-human Cas. Written for the Big Bang Challenge at **spn_verse** , for the trope prompt 'Heat cycles (A/B/O verse)". Yes, the title is from an S Club 7 song. I figured, this is A/B/O threesome heatsex porn, it's not like I was ever going to fool anyone that I have dignity. Thanks to Yalu and Signe_chan for their cheerleading and beta-reading <3

Dean knows something's wrong the second he and Sam get back to the bunker. He's been tired and frustrated from dead-end witnesses all day and he just wants to get out of this crappy Fed suit and pass out, but when he opens the door, this _scent_ hits him and the tiredness evaporates. 

'What the fuck?' Sam says. It must have hit him too - it's potent as hell. Probably the only reason they couldn't smell it outside is how thick the walls and door are. They both push into the war room in a sudden hurry, and Dean hits the lights.

'Hello,' says Cas. Has he been pacing here in the dark this whole time? His eyes are dilated all the way, dark and intense, and he's biting his lip, and if Dean had ever actually ever given any thought to Cas's, y'know, biology - he's an angel, or he was, is biology even relevant? - he'd probably have pegged him as an alpha, maybe a pushy beta, but there's no mistaking that scent. Unbonded omega in heat. 

Dean _feels_ that scent against his skin, breathes deep to taste it, and there's no mistaking his reaction to it, either. Dean and Sam have both pretty much lived on suppressants and birth control pills since puberty. Dad insisted on it. Couldn't have them getting distracted, getting hit by the erratic alpha rut on hunts, or worse, getting someone knocked up. So all their ruts have been planned, controlled, and at least in Dean's case, pretty far away from anyone omega. Maybe it's not the healthiest way to live, but staying on the suppressants has always been easier than trying to factor their cycles into their hit-and-run lifestyle. 

So they do what they've always done. Suppressing things - it's the Winchester way.

But even suppressants can't override proximity to someone so far into their cycle. Dean can feel his body flipping switches already. Dean looks over and Sam's eyes are widening, he's already breathing harder, and Dean knows the same thing's happening to him just from being in the same room as Cas. 

'Cas?' Dean says, making his hands into fists and digging his nails into his palms to stop himself from going over there. He's not an animal. Yeah, he has instincts. Yeah, he wants something. But he's not gonna take it. Being an alpha, it's not an excuse for ... for anything, actually, but 100% not for this. Out of the corner of his eye Dean can see Sam doing the same, shifting, like a dog on a leash. 'Cas, are you -'

'My ves- my body is experiencing an oestrus phase,' Cas says, staring up at them. Dean really badly wants to go down the stairs towards him. 'I need your help.'

 _That doesn't mean what you want it to, this isn't a fucking porno,_ Dean snarls at himself when he feels himself go to take a step forward. Sam lets out a low noise in the back of his throat and his knuckles are white on the railing along the stairs, both hands locked tight around the metal, so hard Dean's almost surprised he isn't bending it. 'Okay,' Dean says, trying to keep his voice steady. 'You need … we can get you stuff to, to take care of this, we can give you space. I mean, we probably shouldn't stay while you're ...' He trails off, unsure. This far gone, Cas won't respond to suppressants, and emergency blockers are only to tide people over til they can get somewhere safe and private. They wouldn't make this go away. 

Dean knows the only thing that'll give Cas any relief now is getting fucked. He needs an alpha or a toy, and it should be his choice which, and fuck, fuck, why did they not give him this talk when he turned human, when it could have just been another orientation lecture and not the most loaded of all loaded questions, with Cas in heat and Dean and Sam getting closer and closer to full-blown rut the longer they spend around him?

'But I want you to stay,' Cas says. Dean swallows hard. 'Both of you,' he adds, and Dean nearly bites through his lip. _Not a porno,_ he reminds himself. _Not a porno, not a porno, not a porno -_

'Do you know what you're asking for?' Sam says. His voice sounds like he gargled gravel. 

'Of course,' Cas says, licking his lips, still staring at them hungrily. He's wearing one of Sam's old shirts, Dean notices, over a pair of Dean's old denims. The clothes are baggy, worn, and they've been out and got Cas new clothes of his own, since he can't just keep miracle-ing the same suit and trenchcoat clean any more, so why is he wearing these now? Dean bites his lip. He likes the look of Cas in those clothes too much. 'I've been waiting for you,' Cas adds, and he's at the foot of the stairs now, gripping the handrail almost as hard as Sam is. 'This morning, I woke and you were gone, but I needed you, so I've been waiting.'

'We can't … take advantage of you like that,' Dean manages, choking on the words because fuck, he wants to, he's got his dander up now, the scent of Cas in the air is so thick it's a taste, honey in the back of Dean's throat, and Sam's a hot, thrumming presence at his side the same way he is when they're about to charge into danger together. But they can't charge into this. They've got to leave, before -

'I am not so impaired by my bodily functions that I can't choose a course of action,' Cas says, high-strung, irritable. 'Otherwise I would have gone into the nearest town in search of relief, wouldn't I? If I were so pushed by hormones to seek stimulation at any cost, why would I wait for you? I haven't ever done this before,' he says, and he starts to stalk up the stairs towards them, wild-eyed and hair messed up like he's already been taken to bed.. 'But I know what it is. I am not innocent, and I'm not weak. I just need _help.'_

He reaches the top of the stairs. The smell of him is overpowering, brainmeltingly good. 'If you'll give it to me,' he adds, and there's one beat, two, of ominous silence. Dean is having trouble processing - what he wants, craves, is warring with all the training of his adult life teaching him he shouldn't take it. Not in these circumstances. This is not how this works. Jesus fuck, he wishes it was this easy.

He's just trying to figure out what the fuck to do, but Cas draws back. 'I … I'm sorry,' he says, and this close Dean can see how strung out he is - it's just the iron control that's so much a part of him, even now, that's letting him still be coherent. He's such a hot freaking mess, he's _shaking_. Dean's body is screaming at him that he knows what Cas needs, that he should give it to him, fast and hard until they're both exhausted, until they're both satisfied. 'I must have misread -'

'You didn't,' Sam says, rough and deep, sensual enough that it's doing things to _Dean_ , no matter what it's doing to Cas, who bites down on a gasp when Sam takes that forward step Dean hasn't. 'Do you really want this?' he asks. 'Because we can help you, but only if that's really what you want.'

'Yes,' Cas says, staring up at Sam with squared shoulders and bright eyes, and Sam reaches out for him. Cas goes into his hold like he was born to be touched. 

'Sam,' Dean says, and Sam looks back at him defiantly. He's all heaving shoulders and dark eyes, and shit, yeah, that's full rut right there, Dean's seen Sam go into it before and it always hits him like this, like a ton of bricks. Dean's a more of a slow-burner than his brother but he can feel it coming for him too, freight-train in a tunnel style. But they can't just - 'Sam, how -'

'Like that girl in St Louis, remember,' Sam says. 'He _needs_ us, Dean.' He's already sliding his fingers up under Cas's hand-me-down shirt, tugging at the hem, and every time skin touches skin Cas rumbles a moan that goes straight to Dean's cock.

'But we can't just -' Dean's stuck on that, stuck on the rules, because picking up a girl who likes threesomes together is different to this, different to hormone-soaked heat-sex - this is special, this is … people _plan_ for their heats, okay, they have to, or life would be goddamn chaos - 

'He only turned human three months ago, Dean, for fuck's sake,' Sam snaps, like he's seeing the problem but his alpha aggression's out in force and he can't bring himself to do this gently. Cas is pushing up against Sam, rubbing off against his hip already like he can't help himself. His jeans are soaked through already, jesus, how long has he been waiting here for them? 'Work it out,' Sam growls.

'Dean, please,' Cas says, and Dean looks at him, really looks at him, and remembers what it was like, rutting for the first time, how out of control he felt, how his dad pretty much gave him a bare-bones talk about it and slapped a box of pills down in front of him and went hunting, left him to it. He'd had to stay in the motel room for two damn weeks til he was sure it was past, jerking off til he was raw, snapping at Sam for the tiniest thing, not knowing what the fuck was going on or what to do about it. Going through that alone, unguided, unhelped? It was hell.

When Sam hit his growth spurt and popped his first knot Dean was freaking _glad_ Dad wasn't there, because it meant Dean could tell Sam all the shit he'd wished someone had told him, just a few years before - that it's normal. That's all - that it's normal. _You're not an animal. You can deal with this. You can do this right._

He's kissing Cas before he knows what he's doing, cupping Cas's face in his hands and pressing their mouths together, licking in soft and hungry, just trying to say _yes_ and _I'm sorry_ and _of course I'll help you, fuck, of course I will_ while Sam drags off bits of their clothing and pulls them down the stairs. Dean's got enough coordination to keep kissing while they maneouvre - doesn't want to stop kissing, ever. Cas is warm and yielding and he makes these tiny noises that Dean wants to eat right out of him.

'Dean,' Cas moans, half into Dean's mouth. He doesn't sound like he wants Dean to stop though, so Dean tugs him back into alignment and slides his tongue back in. 

Sam's hands are huge and hot and forceful, stripping them, directing them. Dean lets him do whatever he wants - Sam's always been better at the long-term strategy. Dean can trust him to do this part, while he takes care of the immediate tactics - strokes through Cas's hair and down the back of his neck and along his newly-naked shoulders, and fuck, wherever seems to make him do that shocky, electric reaction where he gasps and twists in Dean's hold. 

'You ever been with a virgin in heat before?' Sam mutters into Dean's ear as he pulls off his undershirt. It's not pitched like dirty-talk, it's a fucking serious question. Dean pulls away from Cas long enough to let the shirt pass and shake his head, meet his brother's eyes because they need to both be on the same page for this, for the logistics. But they've always worked well as a team, better together than any other two alphas Dean ever heard of. They can do this.

'No,' Dean says, low and quiet. He guides Cas's head to his shoulder, feels him start to lick and suck the skin of his neck while Dean talks. 'You?'

'Yeah,' says Sam, a hint of something shy and defiant in the way he says it. There's a story there.

Dean doesn't have time for a story though, so he doesn't ask, goes for, 'You ever been with a guy?' instead.

'No,' says Sam, and he breaks out into a lopsided smile for a split second. 'Not too old to learn, though. C'mon,' he adds, and tugs them down the hallway. 'Cas, you good?'

'Fine,' Cas bites out against Dean's throat, reaching out blindly and fisting his hand in Sam's shirt. 'Better if this was going faster,' he growls, and yanks Sam in closer. Dean finds himself with an armful of his brother as well as an armful of Cas all of a sudden, and a front-row seat to Cas showing off all his new kissing skills by trying them out on Sam, who shoves his hands down the back of Cas's pants and fucking goes to town. Dean can see where their tongues meet when Cas gasps and Sam smiles against him and pushes in harder. Cas's dick is like iron against Dean's hip, and Sam's pulling his pants down and that smell, that fucking narcotic scent of omega, wanting and ready, is filling the air again.

Dean's so hard he might die from blood-loss to every other goddamn extremity. He wants to snarl at his brother and shove him away but he also wants to snarl at Cas and show Sam what real kissing is, and he can feel his pulse pounding and the heat rising off all of them is like a physical, tangible thing. Sam pulls free of Cas and looks at Dean, and there's none of his usual puppyishness when he grins, fuck no, that's all wolf. 'Feels good, huh?' he says, tilting down to kiss Cas again, perfectly angled to show off for Dean. 'Letting yourself go,' Sam adds. 'Letting yourself have what your body wants. You want this, right Cas?'

'If you don't stop this ridiculous posturing and fuck me, I will find some way to do it myself,' Cas threatens instead of answering. Even standing there mostly-naked and in full-blown heat, he's still not afraid to square up to both of them, and Dean's so hot for him he thinks he might explode, wants to be all over him, wants to be _inside_ him, so fucking bad.

He grabs Cas by the hips and slams him up against the wall and rips his jeans down. 'Oh, I'm gonna fuck you, alright,' he growls, and Cas offers up his throat and kicks off the pants and Dean can feel Sam's teeth close on the back of his neck and the furnace-like heat of his brother as he gets Dean's stupid Fed-suit trousers off. 

'Yeah,' Sam breathes into Dean's ear. 'You're gonna fuck him, and I'm gonna watch, and when you're done, when you've knotted him up good and tight and he's still gagging for cock I'm gonna teach him how to suck mine.'

Cas is watching them both with heavily-hooded eyes, and he smiles like slow-sweet molasses and says, 'And then?'

 _'Fuck_ yeah,' Dean rasps, and hauls Cas back off the wall and shoves him into the bedroom. 'Then, you can have whatever you want,' he promises, when Cas is under him on memory-foam with his thighs spread so wide that Dean's and Sam's knees both fit in the space between, the pair of them like naked nesting dolls, Sam watching with his sharp chin hooked over Dean's shoulder as Dean drags a hand down Cas's body, tweaks at his nipples to see him squirm, see how his cock jerks and drips every time Dean moves somewhere new. 'Let you pop Sam's cherry, maybe, after I've popped yours - wanna see you ride him, Cas, wanna see his face when you make him come in your ass, show him what he's been missing all these years. Or you want one of us to suck you off? Hell, I'll blow you while you're tied off on Sammy, that sound good? Or you wanna try for both of us? Huh?' he asks, brain going a mile a minute, hand finding Cas's dick and stroking, loving the soft, velvet wetness of him, how hard he is, perfect and fucking gorgeous, flushing brighter with every word. 'Two of us, knot you up so good you'll feel it forever, Cas - you'll be so tight, it'll feel so good, your first heat and you're gonna be so good for us, I can taste it.'

Sam reaches under Dean's arm and cradles Cas's cheek in his ginormous palm. 'Fuck, Dean, I think you're killing him,' he murmurs hungrily as Cas nuzzles his fingers. 'You okay there, baby?'

'Need something in me,' Cas says, opening his eyes. There's just the thinnest ring of electric, chain-lightning blue around his blown pupils. 'Feel … feel empty. Hungry. _Need_ you,' he says, pawing at Dean's chest, rolling his head to one side to mouth at Sam's fingers, and Dean feels Sam's cock jump against his ass when Cas takes them all the way in. 

'S'okay, gorgeous, we got you,' Dean says, reaching for his bedside cabinet and the stuff he keeps stashed in there out of force of habit despite the fact that he's not exactly gonna be asking chicks back to their goddamn secret lair. Or dudes, either, he thinks as his hand closes around the box of condoms and pulls them out, puts them on top in easy reach. 'I'm gonna touch you down there now,' he adds, cos you don't just ambush a guy with back-door action, and Cas moans around Sam's fingers. 

Fuck, Cas is soaked, slick as anyone Dean's ever felt - he was half toying with the idea of grabbing the lube he's pretty sure is in his drawer as well as the condoms, cos sometimes even omegas, hell, even omega girls, need a little help in that department, but Cas is wet through, and Dean's first finger circles around and around and up and in without any trouble. 

Cas is still moaning, and Dean looks up to see Sam petting him and letting him suck on his fingers. 'Give him more, Dean,' Sam says in Dean's ear. 'Seriously, dude, he doesn't want the Harlequin romance. He's gagging for it, okay, just fuck him.'

Dean can still feel Sam's dick against his ass every time Sam moves and that should be way weirder than it is - Dean's just so fucking hot for it that even his brother's getting his motor running right now. And that reminds him. He pulls out of Cas's ass and grabs at Sam's wrist, pulls his fingers all spit-shiny and wet from Cas's mouth, same thing both ends, and both Cas and Sam make protesting noises, but Dean's got an idea.

'Need your help, Sam,' Dean growls. 'C'mon. Since you're such an expert,' and he guides Sam's hand down until he gets the idea. 'Just like a girl,' he says, keeps hold of Sam and helps him edge two long, thick fingers into Cas's hole. 'Easier, actually. Tighter. Feel that, Sam? Feel him clench for you?' he says, because Cas is arching now, freer to move and his spine bends like a banana when Sam makes a noise in the back of his throat and flexes his hand. 

'Jesus,' says Sam, like he's been punched in the gut. 

Dean can't help twisting so he can nose Sam's cheek fondly, watch him finger Cas - quick study, Sam is, always was - and watch Cas ride Sam's hand like a cowboy riding a bull. 'Oh Sammy,' Dean breathes. 'I know. Feels so good.'

'This is -' Cas pants, opening his eyes, pushing up on his elbows. 'This is good, but -'

'You want his knot, huh Cas?' Sam says, shoving harder. Cas's eyes slam shut and he keens, and Dean looks down to find Sam's got three fingers in now. 'Want my big brother to fuck the heat out of you, yeah? You all ready for him, baby? You feel ready?'

 _'Need it,'_ Cas rasps, grabbing at Dean's arms, chest, whatever he can reach. 'Fuck me, please fuck me, I need -'

Sam pulls his fingers free and takes hold of Dean's hips instead. 'You heard the guy,' he says. 'Give him what he needs, Dean.' He snags a condom while Dean pets Cas, tries to soothe him.

'Shh, sweetheart,' Dean murmurs, while Cas rolls his hips desperately. 'C'mon, not gonna leave you hanging, I promise, I swear, just hold still for me -' Sam rips the condom open and goes to roll it on Dean - still not weird, and Dean's gonna give that the thought it deserves later - but Cas grabs his wrist.

'Not like that,' he pants. 'Need to feel you.'

Fuck. He ... he can't want that. He can't know what that means. 'No,' Dean grits out, mostly to stop _himself_ , but he still jerks forward instinctively when Cas scrambles for him, feels the head of his dick bump against Cas where he's dripping wet, and Sam shakes Cas off and gets the rubber on, glides his hand down Dean's cock, before that can go any further. _Thank fuck for Sammy,_ what's left of Dean's brain thinks, even though his body tenses, frustrated.

'Next time,' Sam growls, guiding Dean with a hand on his hip and one reaching out to steady Cas. 'But we said we'd take care of you and we're gonna. Dean's gonna fuck you, knot you, gonna scratch that itch so good, Cas -' and Dean's hips are already working in time with his voice, sunk so deep, so fast, in Cas's wet, clinging body, can't do anything else, can't control himself. Sam keeps talking '- but he's gonna do it safe.'

'So full,' Cas mutters thickly, hands fisted tight in the sheets, knees tightening around Dean's body. 'Want more,' he pants. 'Please. Need more. Need ... skin. Taste you, feel -' and he's tossing his head from side to side now, eyes glazed. Dean's been with a lot of people but he's never had someone screw themselves so deep around his cock before, never had someone so wet, so hot, so ready for him. 

'He wants you to breed him,' Sam breathes into Dean's ear. 'Feel that? Smell it? Fuck, he wants knot so fucking badly. Wanna see you give it to him. You want him to put a baby in you, don't you, Cas?' He raises his head and his voice, and Cas's eyes almost roll back in his head. 

'I - I want ... yes,' Cas groans. 'Want to be full, be filled up -'

'Harder, Dean,' Sam snaps, shoving Dean by the hips like he wants to be doing this himself. 'He's in _heat_ , for crap's sake. Your body knows what he needs but you're holding back -' He's pretty much slamming Dean into Cas now, like he's reading both their minds, and Cas is making deep _uh, uh, unnh_ noises in the back of his throat, pushing up into Dean's every thrust. '- stop fucking pussyfooting around and _fuck him.'_

'Fuck,' Dean moans, hips pistoning, orgasm approaching. 'Shut up, shut up -'

'Turn him over,' Sam orders suddenly, pulling away from Dean. 'Hands and knees. Better angle.' Cas really doesn't like it when Sam drags Dean out of his body - fuck, Dean isn't a fan either, he snarls at Sam and almost goes to bite him when he gets too close, mindless and rutting and angry, but Sam growls him down, catches his chin and kisses him hard enough that Dean's lip splits against Sam's teeth, and before Dean can process what's happening Cas is on all fours on the bed, upper body puddled against the sheets and ass presented and Sam licks Dean's blood off his mouth and shoves them back together. 

The slick clutch of Cas around him is enough to make Dean's eyes roll back in his head. Sam was right, like this is better, deeper, and he barely withdraws at all any more, just shoves and shoves and shoves and Cas is right there meeting him, they're grinding together like they're one welded thing, and Sam gets in front of Cas and raises him up, changes the angle and eats the hunger out of his mouth when he cries it out loud.

Dean comes then - Sam and Cas kissing is too much, makes him ache with jealousy and lust and love and Dean's a mess of conflicted alpha instincts in a skin too small to hold it all. His knot swells on the inside of Cas, locks them in together and it's such a sweet, sharp pressure Dean nearly bites through his tongue. Cas scrabbles for grip against the mattress when it happens and Sam holds him still, pushes him up and up until he's sitting in Dean's lap, sitting on his knot, taking it so good, and Dean realises he's saying that out loud. Cas is panting, head hanging. 'So good for us, sweetheart,' Dean's saying, petting down Cas's sides and trying to breathe and kind of not doing so good at it. 

Sam's more use, moving in closer and pulling Cas's head up to look him in the eyes. 'How's it feel?' he asks. 'You okay? You need something else? You need more? Tell me,' he says. 

Dean's still dazed and confused, orgasm whiting out important bits of his brain, but it's suddenly so important to him to hear Cas answer Sam. 'Tell us what you need, Cas,' he says, mouthing at Cas's ear, sliding his hands back down Cas's body because he has to touch him everywhere, has to be all over him as well as in him, has to feel his reactions like they're in the same skin.

Cas make a noise like he's dying; he's so, so hard when Dean's hand finds his cock. Dean's dick twitches hard, and spills more come inside the condom, inside Cas, who shudders and looks up at Sam properly. Sam's looming, naked and hard and breathing like he's run a marathon. He's been so good, been so patient, when the rut has to be burning him from the inside out. Dean's so fucking proud of him, so turned on by him, he only clutches at Cas harder when Sam looks at him all feral-rutting-dominant, and Cas moans for it again, like being between the two of them is the biggest turn-on ever. 'You ever sucked cock before, Cas?' Sam asks, reaching out to touch Cas's face, thumb at his bottom lip where it's bitten hot-red and abused.

'No,' Cas breathes, and Dean's eyes cross because Cas clenches unconsciously when he says it. 

'Jesus Christ,' Dean stutters, watching Sam fumble another condom out and on, and pull Cas forward and down to introduce him to his dick. It changes the angle Dean and Cas meet at, the angle they're joined by, makes Dean jacknife and Cas shudder hotly. 

'Take it slow,' Sam says, voice strained. 'Jeez, I just - I wanna shove it right in, hold it there, make you take it, you got no idea Cas, you're so fucking hot like this, but you're not ready -' He groans, because Cas slides his mouth over the head of his cock and further and further. 'Oh, crap.'

'Looks kinda ready to me,' Dean points out, words hard to form given he can't seem to fucking breathe any more. 'C'mon, dude, it's not that complicated.' Dean's still coming in Cas, can't help the way he shakes and shoves harder in with every pulse of it, and Cas squirms on his lap like he's not complaining at all. Dean watches him flutter his eyes shut and reach out to grab Sam's sharp hip and hold him still while he swears. 'That's it, Cas, take him down nice and easy,' Dean says. He strokes Castiel's shoulder and watches Sam's eyes roll back in his head. 'Yeah, fuck, you're doing good,' he says, kind of to both of them. 'You want it deeper, don't you? Take it,' he urges them both. 'Go on, take it.'

Cas stutters against Dean's body but he does what he's told, stretches out further and Jesus fuck, does he even _have_ a gag reflex? Sam's not exactly got anything to be ashamed of in this department and Cas is just … 

Sam wrenches his eyes open and grabs Cas's head, draws Cas back then pushes into him again. 'Might not have done it before,' he growls, grins, eyes lighting up when he looks at Dean, 'but he's seen it. Or thought about it, maybe. You thought about sucking cock, Cas? Cos sure seems to me like you got the basic idea pretty good.' Jeez, Dean had no idea his brother had such a filthy goddamn mouth. 

Cas hums around Sam. Maybe he wants to answer Sam, even, but Sam's on a roll. He grabs himself around the base of his dick and with the other hand keeps Cas moving. And if the way Cas is driving himself back around Dean, the way he squeezes around Dean's knot, is anything to go by, this is seriously working for him. It takes Sam maybe three more thrusts before he's finished, clamping his hand around his knot and pushing Cas off, curling in on himself as he shakes to pieces.

Cas keens in the back of his throat and shoves himself back up against Dean, catches Sam's heaving shoulders and pulls him into the circle of his arms, so they're all wedged up against each other, Sam's face curled into Cas's shoulder, Cas's hair tickling Dean's ear, their hands all a tangle in between Cas's belly and Sam's. 'Please,' Cas is panting, rocking up and down on Dean, moving easier now because Dean's finally stopped coming, his knot's easing. It'll come free soon, so that he'll be ready for round two, which right now, seeing Cas go nuts like this, is not gonna be far off. 'Please, I need - I don't -' Cas says, broken up. 'There's something - I need something, I need -'

'Shhh,' says Dean, pushing up into him, still hot like burning for him, for the scent of him that's still driving Dean crazy. 'S'okay, Cas, just let me -'

'Not gonna leave you hanging,' Sam croaks, pulling his head up. His eyes are totally glazed, he's still jerking forward hips-first into his hand, in the shadow of Cas's body. 'Gonna make you come, Cas. Gonna be okay.' Around Cas's leaking dick someone else's fingers nudge up against Dean's - Sam's fingers, Sam's hand, Dean'd know that touch anywhere - and they start jerking him off together. 

'There's something missing,' Cas whispers. Dean kisses his temple, speeds up a little. 'Wanted you to come in me,' he adds, and twists so he can bury his face in Dean's neck like he didn't mean to let that one slip, and Dean's gotta pull out of him soon or he's gonna pop another goddamn knot if Cas is gonna keep talking like that, Jesus Christ. This is out of control. 

'Your body thinks it wants a baby,' Sam says, eyes flicking up to Dean's and hand matching Dean's tempo and rhythm, in sync like they always are. 'You don't, Cas, not like this, not gonna risk it,' he says. 'We can get you off without it, I promise.' 

Between them they work Cas until he's sweating and begging and throwing out goddamn orders. Maybe he's omega but he's not rolling over for them, he makes that clear. He grabs for them both over and over, he's leaving fingermarks that are gonna bruise and that's revving Dean's engine like you would not believe, but Sam holds Dean's gaze and they keep touching Cas like this, _safe_ , not giving in even though Dean wants to rip off the condom he's wearing and get back balls-deep and bare in that willing, wanting hole more than almost anything. 

And it takes time, but eventually Cas locks up, every sinew tight and every muscle clenched, and he comes around Dean's cock and all over Sam's tense stomach and their hands in between, and if Dean hadn't already been there, done that, he might think he'd died and gone to Heaven. 

The way Cas sounds, though, when he comes? The way Sam looks at him? The way they're all united, _together,_ like this? That's not Heaven. It's better, a million times better. 

***

Dean learns a lot in the process of helping fuck Cas's heat away. He learns things about Cas, about Sam, that he never even wondered about before. Things like, that Cas takes orders well, gives them better, likes to break them even more than that - mostly that he loves it when you talk to him, he loves being coaxed through an orgasm, loves praise. And Sam's pretty fucking good at providing that, is another thing Dean learns. Sam can run his mouth off in bed like it's an Olympic sport, and then when you think he's the nastiest, kinkiest, dirtiest son of a bitch there ever was, he starts up the cuddling - because Sam's thing, Dean figures out somewhere into day two, is that he likes to figure out what people want and then he likes to give it to them until they beg for mercy. Dean would have felt sorry for Cas, if Cas didn't look so goddamn smug and well-fucked and happy about it.

Another thing Dean learns is that him and Sam? Still make a pretty good team no matter what they're doing. Apparently especially when what they're doing is another person. Tag-team, just like fighting monsters or hustling pool or driving long distance - everything goes better when they play off each other.

Cas's sex-fever broke around midnight last night, maybe - they were down in the dark, all tied up in each other, and he came one last time and then pushed himself away, rather than starting something up again - and they sank into sleep. Now Dean's coming awake again and he can feel days' worth of aches, bites and slap-marks and good old-fashioned overstretched muscles, coming back haunt him. 'Nnngh,' he says incoherently, blinking.

He figures out what woke him when he sees movement in the darkness - over in the corner, near Dean's stack of vinyl, Cas is pulling on his jeans, the ones that used to belong to Dean. 

Dean's not rutting anymore, so he has no excuse for the warm, possessive feeling that settles in his gut, seeing his old worn jeans settle on Cas's hips. They're in pretty good condition, or he wouldn't have given them away, but there's a smear of engine-grease on one thigh and the front beltloop is stretched out from how Dean likes to hook his thumb through it when he's bellying up to a bar or a fight or a game of pool, and it's way, way too good, seeing something so obviously his on Cas. 

Cas hauls on the old grey V-neck of Sam's he'd been wearing with the jeans, and Dean's supposedly-exhausted dick twitches. _Whoa, boy,_ he tells himself. 'Going somewhere?' he asks when Cas turns to the door, realising that he should actually say something rather than let Cas leave like this, even if the view is pretty good. Cas freezes. One other thing they've learnt about him since he lost his grace is that now that he can't just poof out of a room, he's really bad at excusing himself. 

'I woke up,' Cas says, turning back around. 'So I thought I would go and finish the cataloguing I was working on when I went into oestrus.' He shrugs awkwardly.

Dean really badly wants to tell him to come back to bed, but that would push this into 'weird' territory, wouldn't it? Like, if this was a one-time, bros helping each other out in heat thing, then it would be weird for him to want Cas to curl back up with them, right? So he says, 'Yeah, sure,' instead of telling Cas to forget it and just get back in. 

Cas pads out of the room, and Dean settles back down again. Sam mumbles something and rolls onto his back. He snores when he sleeps on his back though, so Dean punches him in the shoulder until he rolls over and makes some goddamn space. He could kick Sam out, but he's not doing any harm and it's not the first time they've shared a bed, so at least _that_ isn't weird. 

He doesn't really sleep, though. He just listens to Sam breathe and drifts. When Cas crawls back into the bed, Dean's about as close to sleep as you can be without actually being asleep, and it takes him a second to work out what's going on. His hand goes for the knife under the pillow, but he's been living in this bunker too long - his reflexes are shot to hell. 

'Shh,' Cas says, settling in between him and Sam, who makes a snuffling noise, face half-buried in the pillow. 'It's only me.'

'Mmm, hey,' Dean says, running his hand down Cas's back and realising he's naked again, and kind of appreciating that more than he should if this is just a helping-each-other-out thing. Which it still could be. Cas's boundaries are still getting built. Dean doesn't wanna assume anything. 'Thought you were working.'

'I was, but I started to worry you would misread my insomnia,' Cas murmurs. He curls up on his side, blinking at Dean in the grey dark. 'You did, didn't you.'

'Been lying there brooding since you left,' Sam mumbles, peeling his face off the pillowcase and burying it in Cas's shoulder instead. Dean glares at him, but he probably doesn't notice. Bitch. 

Cas sighs, and Dean's bare skin prickles where it touches him. 'Sleep, Dean,' Cas orders him softly. 'I'm not going anywhere. If it comforts you to extend that into a metaphor, feel free. It's accurate.'

Sam huffs a soft laugh from the other side of Cas and Dean kind of hates them both but he's sleepy and warm and everything smells of really good sex and the three of them together, so he bites Cas's neck and kicks at Sam's stupid giraffe leg where it's sprawled over Cas and into Dean's territory, and counts that as settling his debts. For now.


End file.
